Junjie Li, M.D., from the University of Leuven in Belgium, and colleagues investigated whether cancer cells (seed) can be killed by selectively destroying by radioactively contaminating their microenvironment (soil) through a dual-targeting approach. A total of 24 rats were implanted with 48 liver rhabdomyosarcomas followed by the administration of 10 mg/kg of CA4P to cause tumor necrosis. The 131I-hypericin, was injected 24 hours after CA4P at 300 MBq/kg. In vivo magnetic resonance imaging, scintigrams, ex vivo gamma counting, autoradiography, and histologic analysis were used to compare tumor responses in the dual-targeting group with that in the vehicle-control and single-targeting (CA4P or 131I-hypericin) groups. Tumor volumes, tumor doubling time (TDT), and radiobiodistribution were estimated.

The investigators found that after eight days of treatment, the tumor volume of rhabdomyosarcomas in the vehicle-control group was five times that of the dual-targeting group, and double that seen in either of the single-targeting groups, with no treatment-related death. The dual-targeting group had a significantly longer TDT. Scintigrams revealed hot spots of necrotic tumor which corresponded with a target-to-liver ratio of 20, and 3.13 percent of the injected dose of 131I-hypericin per gram of tissue.